Biomaterials and Culture Technologies for Regenerative Therapy of Liver Tissue

Oxidized pectin/collagen self-healing hydrogel accelerated the regeneration of acute hepatic injury in a mouse model

The high-rate incidence of hepatic tissue pathologies and lack of enough donors necessitate the development of de novo liver therapeutic protocols and tissue engineering modalities. Due to unique chemical structure, and biological properties, the application of pectin-based hydrogels has been extended in different pathological conditions. Using ozonation [O3 gas (25 mg/h) a flow rate of 1 l/min] for 20, 40, 60, and 80 min, the hepatogenic properties of green synthesized hydrogel containing 6 % oxidized pectin (OP) 1 % collagen (Col) were studied in vitro and acute liver injury mice model. Data confirmed suitable gel content, swelling rate, porosity, Young's modulus, and self-healing capacity of OP-Col hydrogel. Ozonation time can influence the viability and function of human HepG2 cells via the generation-free aldehyde groups in which 40 min-ozonation yielded better biological outcomes (migration↑, and albumin production↑) after neutralization with glycine. The transplantation of glycine-treated liver cells-laden OP-Col hydrogel with 40 min-ozonation protocol reduced the progression of fibrotic changes, and unwanted in situ immune system response in acute liver injury mice model after 14 days. Besides, the systemic levels of albumin and urea were increased coinciding with the reduction of liver cell damage enzymes. OP-based hydrogels can appropriately mimic suitable microenvironments for the regulation of hepatocyte dynamic growth and function in in vitro conditions and following acute injuries. The synthesis of OP-based hydrogel with a specific synthesis protocol promotes the biological activity of transplanted liver cells at the site of injury.

SiO2-based inorganic nanofiber aerogel with rapid hemostasis and liver wound healing functions

Non-compressible hemostasis and promoting tissue healing are important in soft tissue trauma repair. Inorganic aerogels show superior performance in rapid hemostasis or promoting tissue healing, but simultaneously promoting non-compressive hemostasis and soft tissue healing still remains a challenge. Herein, SiO2-based inorganic nanofiber aerogels (M2+@SiO2, M=Ca, Mg, and Sr) were prepared by freeze-drying the mixture of bioactive silicates-deposited SiO2 nanofibers and SiO2 sol. These M2+@SiO2 aerogels have a three-dimensional highly-interconnected porous structure, remarkable flexibility, high absorption, good hydrophilicity, negative zeta potential, and bioactive ions releasing capacity. M2+@SiO2 aerogels not only exhibited satisfactory hemostasis activities in vitro, but also possessed high hemostatic efficacy in compressible rabbit femoral artery injury bleeding model and non-compressible rat liver puncture bleeding model compared to medical gauze and gelatin sponge. M2+@SiO2 aerogel had low blood clotting index of Ca. 10 % and short partial thromboplastin time of ca. 82 s in vitro, and could greatly short bleeding time by >50 % and decrease blood loss by about 80 % compared to medical gauze and gelatin sponge in non-compressible hemostasis. Sr2+@SiO2 aerogel showed optimal bioactivities on promoting cell proliferation, cell migration, and the expression of liver function and angiogenesis related genes and proteins in vitro. Importantly, Sr2+@SiO2 aerogel possessed a noteworthy function to promote liver soft tissue healing in vivo by releasing bioactive ions and providing a highly-interconnected porous structure to support vascular development and tissue regeneration. Overall, Sr2+@SiO2 aerogel has great potential for integrated rapid hemostasis and soft tissue healing, which is promising in soft tissue trauma therapy. STATEMENT OF SIGNIFICANCE: Non-compressible hemorrhage and soft tissue impairment are the main causes of mortality in emergency trauma. Inorganic aerogels with high porosity and outstanding flexibility can rapidly absorb blood to pro-coagulation and fill in irregular trauma without compression, but the low bioactivity limited the ability to promote soft tissue healing. Herein, SiO2-based inorganic nanofiber aerogels (M2+@SiO2, M=Ca, Mg, and Sr) were prepared by freeze-drying the mixture of bioactive silicates-deposited SiO2 nanofibers and SiO2 sol. M2+@SiO2 aerogels possessed high bioactivity and exhibited superior hemostatic performance in compressible and non-compressible bleeding model. Furthermore, Sr2+@SiO2 aerogel showed optimal bioactivities on cell responses and effectively promoted liver healing by releasing bioactive ions and providing highly-interconnected porous support structure for vascular development and tissue regeneration.

The Complementary Roles of Neurological and Musculoskeletal Physical Therapy and Regenerative Medicine: A Comprehensive Review

Regenerative medicine, encompassing various therapeutic approaches aimed at tissue repair and regeneration, has emerged as a promising field in the realm of physical therapy. Aim: This comprehensive review seeks to explore the evolving role of regenerative medicine within the domain of physical therapy, highlighting its potential applications, challenges, and current trends. Researchers selected publications of pertinent studies from 2015 to 2024 and performed an exhaustive review of electronic databases such as PubMed, Embase, and Google Scholar using the targeted keywords "regenerative medicine", "rehabilitation", "tissue repair", and "physical therapy" to screen applicable studies according to preset parameters for eligibility, then compiled key insights from the extracted data. Several regenerative medicine methods that are applied in physical therapy, in particular, stem cell therapy, platelet-rich plasma (PRP), tissue engineering, and growth factor treatments, were analyzed in this research study. The corresponding efficacy of these methods in the recovery process were also elaborated, including a discussion on facilitating tissue repair, alleviating pain, and improving functional restoration. Additionally, this review reports the challenges concerning regenerative therapies, among them the standardization of protocols, safety concerns, and ethical issues. Regenerative medicine bears considerable potential as an adjunctive therapy in physiotherapy, providing new pathways for improving tissue repair and functional results. Although significant strides have been made in interpreting the potential of regenerative techniques, further research is warranted to enhance protocols, establish safety profiles, and increase access and availability. Merging regenerative medicine into the structure of physical therapy indicates a transformative alteration in clinical practice, with the benefit of increasing patient care and improving long-term results.

The impact of matrix stiffness on hepatic cell function, liver fibrosis, and hepatocellular carcinoma-Based on quantitative data

Over the past few decades, extensive research has explored the development of supportive scaffold materials for in vitro hepatic cell culture, to effectively mimic in vivo microenvironments. It is crucial for hepatic disease modeling, drug screening, and therapeutic evaluations, considering the ethical concerns and practical challenges associated with in vivo experiments. This review offers a comprehensive perspective on hepatic cell culture using bioscaffolds by encompassing all stages of hepatic diseases-from a healthy liver to fibrosis and hepatocellular carcinoma (HCC)-with a specific focus on matrix stiffness. This review begins by providing physiological and functional overviews of the liver. Subsequently, it explores hepatic cellular behaviors dependent on matrix stiffness from previous reports. For hepatic cell activities, softer matrices showed significant advantages over stiffer ones in terms of cell proliferation, migration, and hepatic functions. Conversely, stiffer matrices induced myofibroblastic activation of hepatic stellate cells, contributing to the further progression of fibrosis. Elevated matrix stiffness also correlates with HCC by increasing proliferation, epithelial-mesenchymal transition, metastasis, and drug resistance of HCC cells. In addition, we provide quantitative information on available data to offer valuable perspectives for refining the preparation and development of matrices for hepatic tissue engineering. We also suggest directions for further research on this topic.

Scaffold-mediated liver regeneration: A comprehensive exploration of current advances

The liver coordinates over 500 biochemical processes crucial for maintaining homeostasis, detoxification, and metabolism. Its specialized cells, arranged in hexagonal lobules, enable it to function as a highly efficient metabolic engine. However, diseases such as cirrhosis, fatty liver disease, and hepatitis present significant global health challenges. Traditional drug development is expensive and often ineffective at predicting human responses, driving interest in advanced in vitro liver models utilizing 3D bioprinting and microfluidics. These models strive to mimic the liver's complex microenvironment, improving drug screening and disease research. Despite its resilience, the liver is vulnerable to chronic illnesses, injuries, and cancers, leading to millions of deaths annually. Organ shortages hinder liver transplantation, highlighting the need for alternative treatments. Tissue engineering, employing polymer-based scaffolds and 3D bioprinting, shows promise. This review examines these innovative strategies, including liver organoids and liver tissue-on-chip technologies, to address the challenges of liver diseases.

Combination of melt-electrospun poly-ε-caprolactone scaffolds and hepatocyte-like cells from footprint-free hiPSCs to create 3D biohybrid constructs for liver tissue engineering

The liver is a vital organ with numerous functions, including metabolic functions, detoxification, and the synthesis of secretory proteins. The increasing prevalence of liver diseases requires the development of effective treatments, models, and regenerative approaches. The field of liver tissue engineering represents a significant advance in overcoming these challenges. In this study, 3D biohybrid constructs were created by combining hepatocyte-like cells (HLCs) derived from patient-specific footprint-free human induced pluripotent stem cells (hiPSCs) and 3D melt-electrospun poly-ε-caprolactone (PCL) scaffolds. First, a differentiation procedure was established to obtain autologous HCLs from hiPSCs reprogrammed from renal epithelial cells using self-replicating mRNA. The obtained cells expressed hepatocyte-specific markers and exhibited important hepatocyte functions, such as albumin synthesis, cytochrome P450 activity, glycogen storage, and indocyanine green metabolism. Biocompatible PCL scaffolds were fabricated by melt-electrospinning and seeded with pre-differentiated hepatoblasts, which uniformly attached to the fibers of the scaffolds and successfully matured into HLCs. The use of patient-specific, footprint-free hiPSC-derived HLCs represents a promising cell source for personalized liver regeneration strategies. In combination with biocompatible 3D scaffolds, this innovative approach has a broader range of applications spanning liver tissue engineering, drug testing and discovery, and disease modeling.

Mechanistic Understanding of Idiosyncratic Drug-Induced Hepatotoxicity Using Co-Cultures of Hepatocytes and Macrophages

Hepatotoxicity or drug-induced liver injury (DILI) is a major safety issue in drug development as a primary reason for drug failure in clinical trials and the main cause for post-marketing regulatory measures like drug withdrawal. Idiosyncratic DILI (iDILI) is a patient-specific, multifactorial, and multicellular process that cannot be recapitulated in current in vitro models; thus, our major goal is to develop and fully characterize a co-culture system and to evaluate its suitability for predicting iDILI. For this purpose, we used human hepatoma HepG2 cells and macrophages differentiated from a monocyte cell line (THP-1) and established the appropriate co-culture conditions for mimicking an inflammatory environment. Then, mono-cultures and co-cultures were treated with model iDILI compounds (trovafloxacin, troglitazone) and their parent non-iDILI compounds (levofloxacin, rosiglitazone), and the effects on viability and the mechanisms implicated (i.e., oxidative stress induction) were analyzed. Our results show that co-culture systems including hepatocytes (HepG2) and other cell types (THP-1-derived macrophages) help to enhance the mechanistic understanding of iDILI, providing better hepatotoxicity predictions.

Design of functional biomaterials as substrates for corneal endothelium tissue engineering

Corneal endothelium defects are one of the leading causes of blindness worldwide. The actual treatment is transplantation, which requires the use of human cadaveric donors, but it faces several problems, such as global shortage of donors. Therefore, new alternatives are being developed and, among them, cell therapy has gained interest in the last years due to its promising results in tissue regeneration. Nevertheless, the direct administration of cells may sometimes have limited success due to the immune response, hence requiring the combination with extracellular mimicking materials. In this review, we present different methods to obtain corneal endothelial cells from diverse cell sources such as pluripotent or multipotent stem cells. Moreover, we discuss different substrates in order to allow a correct implantation as a cell sheet and to promote an enhanced cell behavior. For this reason, natural or synthetic matrixes that mimic the native environment have been developed. These matrixes have been optimized in terms of their physicochemical properties, such as stiffness, topography, composition and transparency. To further enhance the matrixes properties, these can be tuned by incorporating certain molecules that can be delivered in a sustained manner in order to enhance biological behavior. Finally, we elucidate future directions for corneal endothelial regeneration, such as 3D printing, in order to obtain patient-specific substrates.

Alginate-chitosan core-shell microcapsule cultures of hepatic cells in a small scale stirred bioreactor: impact of shear forces and microcapsule core composition

A small scale stirred bioreactor was designed and the effect of different agitation rates (30, 60 and 100 rpm) was investigated on HepG2 cells cultured in alginate-chitosan (AC) core-shell microcapsule in terms of the cell proliferation and liver-specific function. The microencapsulated hepatic cells could proliferate well when they were cultured for 10 days at 30 rpm while the cell-laden microcapsules showed no cell proliferation at 100 rpm in the bioreactor system. Albumin production rate, as an important liver function, increased also 1.8- and 1.5- fold under stirring rate of 30 rpm compared to the static culture and 60 rpm of agitation, respectively. Moreover, In comparison with the static culture, about 1.5-fold increment in urea production was observed at 30 rpm. Similarly, the highest expressions of albumin and P450 genes were found at 30 rpm stirring rate, which were 4.9- and 19.2-fold of the static culture. Addition of collagen to the microcapsule core composition (ACol/C) could improve the cell proliferation and functionality at 60 rpm in comparison with the cell-laden microcapsules without collagen. The study demonstrated the hepatic cell-laden ACol/C microcapsule hydrogel cultured in the small scale stirred bioreactor at low mixing rate has a great potential for mass production of the hepatic cells while maintaining liver-specific functions.

SARS-CoV-2 and tissue damage: current insights and biomaterial-based therapeutic strategies

The effect of SARS-CoV-2 infection on humanity has gained worldwide attention and importance due to the rapid transmission, lack of treatment options and high mortality rate of the virus. While scientists across the world are searching for vaccines/drugs that can control the spread of the virus and/or reduce the risks associated with infection, patients infected with SARS-CoV-2 have been reported to have tissue/organ damage. With most tissues/organs having limited regenerative potential, interventions that prevent further damage or facilitate healing would be helpful. In the past few decades, biomaterials have gained prominence in the field of tissue engineering, in view of their major role in the regenerative process. Here we describe the effect of SARS-CoV-2 on multiple tissues/organs, and provide evidence for the positive role of biomaterials in aiding tissue repair. These findings are further extrapolated to explore their prospects as a therapeutic platform to address the tissue/organ damage that is frequently observed during this viral outbreak. This study suggests that the biomaterial-based approach could be an effective strategy for regenerating tissues/organs damaged by SARS-CoV-2.

Biomaterial-based cell delivery strategies to promote liver regeneration

Chronic liver disease and cirrhosis is a widespread and untreatable condition that leads to lifelong impairment and eventual death. The scarcity of liver transplantation options requires the development of new strategies to attenuate disease progression and reestablish liver function by promoting regeneration. Biomaterials are becoming an increasingly promising option to both culture and deliver cells to support in vivo viability and long-term function. There is a wide variety of both natural and synthetic biomaterials that are becoming established as delivery vehicles with their own unique advantages and disadvantages for liver regeneration. We review the latest developments in cell transplantation strategies to promote liver regeneration, with a focus on the use of both natural and synthetic biomaterials for cell culture and delivery. We conclude that future work will need to refine the use of these biomaterials and combine them with novel strategies that recapitulate liver organization and function in order to translate this strategy to clinical use.

Fe (III)@TA@IGF-2 microspheres loaded hydrogel for liver injury treatment

As one of the most commonly used materials in liver tissue engineering, hydrogel has received much attention in recent years. In this work, we prepared a gelatin methacrylate (GelMA)/oxidized hyaluronic acid (OHA)/galactosylated chitosan (Gal-CS)/Fe (III)@TA@IGF-2 200 (TA200) hydrogel loaded with insulin-like growth factor 2 (IGF-2) for regeneration of damaged hepatocytes. Fe (III)@TA microspheres served as carrier to achieve sustained release of IGF-2 to promote hepatocytes regeneration. Galactose ligands could bind to the asialoglycoprotein receptor (ASGPR) on the surface of hepatocytes. Galactosylated chitosan could significantly increase the specific function of hepatocytes. The hydrogel we prepared had a storage modulus of 1100 Pa and was suitable for migration of hepatocytes. The release ratio of IGF-2 could reach up to 90% within 14 days. For carbon tetrachloride (CCl₄) induced human hepatic stellate cell line LX2 damage, GelMA/OHA/Gal-CS/TA200 hydrogel could significantly improve the survival of LX2 cells. The expression of HNF-4α and transferrin was detected in LX2 cells treated with hydrogel, indicating that the specific function of the liver was also restored. In summary, the GelMA/OHA/Gal-CS/TA200 hydrogels could be used as new tissue engineering scaffolds for the construction of artificial livers.

Advanced Biomaterials and Processing Methods for Liver Regeneration: State-of-the-Art and Future Trends

Liver diseases contribute markedly to the global burden of mortality and disease. The limited organ disposal for orthotopic liver transplantation results in a continuing need for alternative strategies. Over the past years, important progress has been made in the field of tissue engineering (TE). Many of the early trials to improve the development of an engineered tissue construct are based on seeding cells onto biomaterial scaffolds. Nowadays, several TE approaches have been developed and are applied to one vital organ: the liver. Essential elements must be considered in liver TE-cells and culturing systems, bioactive agents or growth factors (GF), and biomaterials and processing methods. The potential of hepatocytes, mesenchymal stem cells, and others as cell sources is demonstrated. They need engineered biomaterial-based scaffolds with perfect biocompatibility and bioactivity to support cell proliferation and hepatic differentiation as well as allowing extracellular matrix deposition and vascularization. Moreover, they require a microenvironment provided using conventional or advanced processing technologies in order to supply oxygen, nutrients, and GF. Herein the biomaterials and the conventional and advanced processing technologies, including cell-sheets process, 3D bioprinting, and microfluidic systems, as well as the future trends in these major fields are discussed.

3D spheroids generated on carbon nanotube-functionalized fibrous scaffolds for drug metabolism and toxicity screening

The mechanical and electrical stimuli have a profound effect on the cellular behavior and function. In this study, a series of conductive nanofibrous scaffolds are developed by blend electrospinning of poly(styrene-co-maleic acid) (PSMA) and multiwalled-carbon nanotubes (CNTs), followed by grafting galactose as cell adhesion cues. When the mass ratios of CNTs to PSMA increase up to 5%, the alignment, Young's modulus and conductivity of fibrous scaffolds increase, whereas the average diameter, pore size and elongation at break decrease. Primary hepatocytes cultured on the scaffolds are self-assembled into 3D spheroids, which restores the hepatocyte polarity and sufficient expression of drug metabolism enzymes over an extended period of time. Among these conductive scaffolds, hepatocytes cultured on fibers containing 3% of CNTs (F3) show the highest clearance rates of model drugs, offering a better prediction of the in vivo data with a high correlation value. Moreover, the drug metabolism capability is maintained over 15 days and is more sensitive towards the inducers and inhibitors of metabolizing enzymes, demonstrating the applicability for drug-drug interaction studies. Thus, this culture system has been demonstrated as a reliable in vitro model for high-throughput screening of metabolism and toxicity in the early phases of drug development.

Collagen modulates functional activity of hepatic cells inside alginate-galactosylated chitosan hydrogel microcapsules

To provide comparable hepatic tissue microenvironment and induce functional behavior for hepatocytes, galctosylated-chitosan (GC) as well as collagen (Col) was added to alginate microcapsule coated with extra layer of chitosan. Four different hydrogel groups of alginate/chitosan (AC); alginate-galactosylated chitosan/chitosan (AGC/C); alginate-collagen/chitosan (ACol/C); and alginate-galactosylated chitosan-collagen/chitosan (AGCCol/C) were prepared and characterized for physical properties such as porosity, swelling, degradation rate, and stiffness. Introduction of GC as well as Col to alginate regulated significantly the physical properties of the resultant hydrogels. GC addition decreased dramatically swelling, degradation, pore size and mechanical properties of the resultant hydrogel. However, the influence of GC on the physical properties in the presence of Col (AGCCol/A) was in a reverse manner, as compared to the AGC/C hydrogel. The AGCCol/C microenvironment also promoted proliferation of microencapsulated HepG2 cells, as a model of hepatocyte, compared to the control-matched groups. Biochemical analysis after 10 days revealed a superior effect of AGCCol/C on the secretion of albumin and urea compared to other groups (P < 0.05). These features were coincided with the mRNA up-regulation of P450 and albumin in the AGCCol/C groups compared to the AGC/C and ACol/C groups (P < 0.05). The study demonstrated that enrichment of alginate-based hydrogels with Col and GC could be touted as an appropriate 3D platform for modular hepatic tissue engineering.

Hydrogels for Liver Tissue Engineering

Bioengineered livers are promising in vitro models for drug testing, toxicological studies, and as disease models, and might in the future be an alternative for donor organs to treat end-stage liver diseases. Liver tissue engineering (LTE) aims to construct liver models that are physiologically relevant. To make bioengineered livers, the two most important ingredients are hepatic cells and supportive materials such as hydrogels. In the past decades, dozens of hydrogels have been developed to act as supportive materials, and some have been used for in vitro models and formed functional liver constructs. However, currently none of the used hydrogels are suitable for in vivo transplantation. Here, the histology of the human liver and its relationship with LTE is introduced. After that, significant characteristics of hydrogels are described focusing on LTE. Then, both natural and synthetic materials utilized in hydrogels for LTE are reviewed individually. Finally, a conclusion is drawn on a comparison of the different hydrogels and their characteristics and ideal hydrogels are proposed to promote LTE.

Poly(butylene terephthalate) Fiber Assembly with Controllable Pore Size and Gradient Wettability: Potential in Simplifying Cell Culture Procedure

This study reports the scalable fabrication of a poly(butylene terephthalate) fiber assembly featured with controllable pore size and gradient wettability. Pore size is controlled via adjusting the throughput of melt blown process, while gradient wettability is achieved through single-sided plasma exposure and subsequent chitosan coating. When used in cell culture, the fiber assembly takes much less time in reaching a high cell collecting/releasing rate up to ≥99.5%, which is similar to that of the conventional centrifugal method. Other advantages of the fiber assembly, such as improved cell viability, reduced risk of contamination, and excellent reusability are also proved, leading us to believe its great potential in making the current cell culture procedure simpler and faster.

Hepatocyte culture on 3D porous scaffolds of PCL/PMCL

The development of three-dimensional (3D) porous scaffolds for soft tissue engineering mainly focused on manipulation of scaffold properties with cell behaviors. By emulsion freeze-drying method, four types of porous scaffolds were prepared from amorphous poly(4-methy-ε-caprolactone) (PMCL) and semi-crystalline poly(ε-caprolactone) (PCL) at different weight ratios, named as PMCL0, PMCL30, PMCL50 and PMCL70, respectively. Visual observation on cross-sectional images of the scaffolds appeared as sponge-like materials with three-dimensional and highly porous morphologies. However, the pore size, porosity and wettability of blends were not decreased linearly with increasing amorphous PMCL. Distinguished from PMCL30 or PMCL70, PMCL50 preserved intact PCL crystals distributed in amorphous matrix, resulting in the lowest Young's modulus (E) and relatively high wettability. From in vitro cell culture, it was observed that PMCL50 scaffold supported human induced hepatocytes (hiHeps) proliferation and function preservation best among all scaffolds. hiHeps on PMCL50 inclined to adopt fibroblastic morphology, whereas formed spheroidal morphology on PMCL0. It was suggested that our bare scaffolds with tailored properties have shown remarkable capability towards hiHep proliferation and function expression.

From supramolecular polymers to multi-component biomaterials

The most striking and general property of the biological fibrous architectures in the extracellular matrix (ECM) is the strong and directional interaction between biologically active protein subunits. These fibers display rich dynamic behavior without losing their architectural integrity. The complexity of the ECM taking care of many essential properties has inspired synthetic chemists to mimic these properties in artificial one-dimensional fibrous structures with the aim to arrive at multi-component biomaterials. Due to the dynamic character required for interaction with natural tissue, supramolecular biomaterials are promising candidates for regenerative medicine. Depending on the application area, and thereby the design criteria of these multi-component fibrous biomaterials, they are used as elastomeric materials or hydrogel systems. Elastomeric materials are designed to have load bearing properties whereas hydrogels are proposed to support in vitro cell culture. Although the chemical structures and systems designed and studied today are rather simple compared to the complexity of the ECM, the first examples of these functional supramolecular biomaterials reaching the clinic have been reported. The basic concept of many of these supramolecular biomaterials is based on their ability to adapt to cell behavior as a result of dynamic non-covalent interactions. In this review, we show the translation of one-dimensional supramolecular polymers into multi-component functional biomaterials for regenerative medicine applications.